Electron emission source, electric device using the same, and method of manufacturing the electron emission source

ABSTRACT

Provided are an electron emission source, a display apparatus using the same, an electronic device, and a method of manufacturing the display apparatus. The electron emission source includes a substrate, a cathode separately manufactured from the substrate, and a needle-shaped electron emission material layer, e.g., carbon nanotube (CNT) layer, fixed to the cathode by an adhesive layer. The CNT layer is formed by a suspension filtering method, and electron emission density is increased by a subsequent taping process on the electron emission material layer.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a divisional application of U.S. application Ser.No. 12/129,005, filed on May 29, 2008, which claims the benefit ofKorean Patent Application No. 10-2008-0019298, filed on Feb. 29, 2008,in the Korean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electron emission source, anelectric device using the same, and a method of manufacturing theelectron emission source, and more particularly, to an electron emissionsource using a needle-shaped electron emission material such as carbonnanotubes (CNT).

2. Description of the Related Art

Carbon nanotubes (CNTs) or nanoparticles are preferred as electronemission materials of electron emission sources. CNTs refer to tubularmolecules composed primarily of carbons. There are various types of CNTsaccording to shapes. CNTs have very good electrical, mechanical,chemical, and thermal properties, and thus are applied to variousfields. CNTs have a low work function and a high aspect ratio. Since theradius of curvature at a top end or emission end is small, CNTs have avery high field enhancement factor, thereby making it possible to emitelectrons at a low electric field.

Conventional methods of manufacturing a CNT electron emission source areroughly divided into a method of vertically growing CNTs directly on aconductor, such as a cathode or a substrate, and a method of attachingCNT powder, which is separately synthesized, to a cathode.

Examples of the method of vertically growing the CNTs directly on theconductor includes a lot of methods that involve vertically aligningCNTs on various cathode substrates, on which catalytic metal particlesare deposited, through decomposition of carbon source gas at hightemperature (refer to Science vol. 283, 512, 1999; Chemical PhysicsLetters. 312, 461, 1999; Chemical Physics Letters. 326, 175, 2000; NanoLetter vol. 5, 2153, 2005; US006350488B1; and US006514113B1).

Examples of the method of attaching the synthesized CNT powder to thecathode include suspension filtering, screen printing, electrophoresis,self-assembly, spraying, and inkjet printing.

A suspension filtering method involves filtering a CNT suspensionthrough filter paper having pores and transferring the filtered CNTsuspension to a cathode substrate coated with Teflon (refer to Sciencevol. 268, 845, 1995, and Applied Physics Letters vol. 73, 918, 1998).

A screen printing involves printing and firing paste, which is formed bymixing CNT powder with a vehicle containing a polymer and an organicsolvent, an inorganic binder, and other additives, on a cathodesubstrate to form a CNT thin film (refer to Applied Physics Letters vol.75, 3129, 1999, and Korean Patent Publication No. 10-2007-0011808).

An electrophoresis method involves loading a cathode substrate in anelectrolyte solution containing a surfactant and CNT powder andattaching CNT particles to the cathode substrate by usingelectrophoresis (refer to Advanced Materials vol. 13, 1770, 2001; NanoLetter vol. 6, 1569, 2006; US006616497B1; and US20060055303A1.

A self-assembly method involves vertically dipping a hydrophilicsubstrate in a suspension where CNTs whose surfaces are modified tohydrophilic are dispersed in deionized water to form a CNT thin filmthrough slow evaporation (refer to Advanced Materials vol. 14, 8990,2002; and US006969690B2).

A spraying method involves spraying an evenly dispersed CNT suspensionthrough a spray nozzle to form a CNT thin film on a cathode substrate(refer to Mat. Res. Soc. Symp. Proc. vol. 593, 215, 2000; Carbon vol.44, 2689, 2006; the Journal of Physical Chemistry C.111, 4175, 2007;US006277318B1; and Korean Patent Publication No. 10-2007-0001769).

An inkjet printing method involves printing an evenly dispersed CNTsuspension on a cathode substrate by using an inkjet printer to form aCNT thin film (refer to Small. vol. 2, 1021, 2006; Carbon vol. 45,27129, 2007; and US20050202578A1).

In detail, a method of directly vertically growing CNTs comprisesdepositing a nano-sized catalytic metal on a conductive ornon-conductive cathode substrate through sputtering, thermal deposition,electron (E)-beam evaporation, or the like, thermally decomposing carbonsource gas, that is, a gaseous or liquid hydrocarbon, at hightemperature through chemical vapor deposition (CVD), and manufacturingan vertically aligned CNT field electron emission source. This methodhas advantages in that it is easy to control the diameter, length,density, and pattern of the CNTs, but has disadvantages in that it isdifficult to ensure high uniformity and control the particle size of thecatalytic metal when the catalytic metal is deposited over a large area,adhesion between the grown CNTs and the cathode substrate is weak, andit is not easy to manufacture a large CNT field electron emissionsource.

In order to solve the weak adhesion between the CNTs and the cathodesubstrate and the difficulty in manufacturing the large CNT fieldelectron emission source, various methods of purifying, dispersing, andfunctionalizing synthesized CNT power into paste or dispersingsynthesized CNT in a solvent and a surfactant to form a suspension andattaching CNTs to a cathode substrate have been developed. Among thevarious methods, a screen printing method of printing CNT paste, whichincludes CNT powder, a polymer, a binder, an organic solvent, a metalfiller, and other additives, on a cathode substrate and manufacturing aCNT electron emission source through drying, exposure, firing, surfaceprotrusion process, and so on has advantages in that adhesion betweenthe cathode substrate and the CNT electron emission source is strong anda large CNT electron emission source can be manufactured, but hasdisadvantages in that it is difficult to control the density of anactive electron emission site, field electron emission characteristicsare easily deteriorated due to the variety of organic and inorganicbinders and polymers, and a manufacturing process is complicated. Anelectrophoresis method of mixing CNT powder with a dispersing agent inan electrolyte solution to form an evenly dispersed CNT suspension,loading two electrode substrates in the CNT suspension to form anelectric field, depositing CNTs positively charged in the electric fieldon a cathode substrate to which a negative voltage is applied tomanufacture a CNT field electron emission source has advantages in thatselective deposition can be made at room temperature and a large CNTfield electron emission source can be manufactured, but hasdisadvantages in that it is difficult to control thickness and density,uniformity and reproduction are poor, and adhesion between the CNTs andthe cathode substrate is weak, thereby reducing reliability andstability during field electron emission.

A self-assembly method of vertically dipping a hydrophilic cathodesubstrate in a suspension where CNTs whose surfaces are modified tohydrophilic are dispersed in deionized water to form a CNT fieldelectron emission source through slow evaporation has advantages in thata manufacturing process is simple and the CNT field electron emissionsource can be easily made large at room temperature, but hasdisadvantages in that adhesion between a CNT thin film and the cathodesubstrate is weak, like the electrophoresis method, and lots of time isrequired.

A spraying method has advantages in that a manufacturing process issimple and a large CNT field electron emission source can be easilymanufactured at room temperature, but has disadvantages in that, sincethe state of a surface of a CNT thin film is determined by the amount ofsuspension that evaporates while the suspension is sprayed from a nozzleto a cathode substrate, it is difficult to control the thickness anddensity of the CNT thin film, it is also difficult to uniformly depositthe CNT thin film, which results in low uniformity and reproduction, andadhesion between the CNT thin film and the cathode substrate is weak,which leads to easy detachment during electric field electron emission.

An inkjet printing method of selectively printing a suspension, which isformed by evenly dispersing CNT powder whose surface is modified tohydrophilic in deionized water, on a cathode substrate to form a CNTfield electron emission source had advantages in that it is easy tocontrol the thickness and density of a CNT thin film, and the CNT thinfilm can be selectively patterned and can be made large at roomtemperature, but has disadvantages in that adhesion between the printedCNT field electron emission source and the cathode substrate is weak. Asuspension filtering method of filtering an evenly dispersed CNTsuspension through filter paper having pores, and simply transferringthe filtered CNT suspension to a cathode surface coated with Teflon toform a CNT field electron emission source has advantages in that it iseasy to control the thickness and density of a CNT thin film bycontrolling the amount or density of CNT powder, a manufacturing processis simple, and a large CNT field electron emission source can bemanufactured, but has disadvantages in that adhesion between the CNTthin film and the cathode substrate is weak.

As a modification of the suspension filtering method of forming the CNTthin film and then transferring the CNT thin film to the cathodesubstrate, a method of bonding a CNT thin film, which is directly grownand vertically aligned, to a layer where conductive silver paste ispatterned, thermally compressing the CNT thin film, and transferring theresultant CNT thin film to a metal substrate, or preparing a patternedconductive layer on a glass sheet, depositing conductive carbon paste,such as, silver or gold paste, on the conductive layer, and transferringCNTs, which are moved from a CNT thin film, which is directly grown andvertically aligned, to an adhesion sheet, to the conductive pastedeposited on the conductive layer to form a CNT field electron emissionsource is disclosed in US 2004/0166235 A1. However, this method hasdisadvantages in that it is difficult to manufacture a large CNT thinfilm because the CNT thin film is directly grown and vertically aligned,and a manufacturing process is complicated because drying, compression,and heating, or thermal compression, should be performed to ensure highadhesion when the CNTs are transferred.

In manufacturing a good CNT electron emission source, high reliability,high stability, and low cost should be ensured. Impurities badlyaffecting electron emission should not be mixed. The density of CNTsshould be easily controlled for high uniformity and reproduction.Adhesion between the CNTs and a cathode supporting the CNTs should behigh enough to ensure reliability and stability of the CNT electronemission source. Also, a manufacturing processes should be simple toreduce manufacturing costs and a large CNT electron emission sourceshould be able to be manufactured.

SUMMARY OF THE INVENTION

The present invention provides an electron emission source with highreliability that can be easily manufactured, a display apparatus usingthe electron emission source, and methods of manufacturing the electronemission source and the display apparatus.

According to an aspect of the present invention, there is provided anelectron emission source comprising: a conductive plate-shaped cathode;a needle-shaped electron emission material layer formed on a surface ofthe cathode; a base supporting the cathode; and a fixing element fixingthe cathode to the base.

An adhesive layer for fixing the electron emission material layer to aconductive tape may be interposed between the electron emission materiallayer and the conductive tape.

The fixing element may be any one of a fixing member, an adhesive, and awelding portion which mechanically fix the conductive tape to the base.

The base supporting the cathode and the fixing member fixing the cathodeto the base may be complementarily engaged with each other. A protrusioncorresponding to the electron emission material layer may be formed onthe base, and the fixing member has a frame shape and is fitted aroundthe protrusion.

According to another aspect of the present invention, there is provideda method of manufacturing an electron emission source, the methodcomprising: forming an electron emission material layer on a template;transferring the electron emission material layer to a plate-shapedcathode on which an adhesive layer is formed and fixing the electronemission material layer to the cathode; and performing a taping processon the electron emission material layer transferred to the cathode toerect electron emission materials with respect to the cathode.

The plate-shaped template may be a filter template having a plurality ofpores. The forming of the electron emission material layer may comprise:applying a suspension in which electron emission materials are dispersedonto the template; and drying the suspension.

The performing of the taping process may comprise pressing an erectingmember having adhesion to the electron emission materials against theelectron emission materials, and separating the erecting member from theelectron emission materials, to erect the electron emission materialswith respect to the cathode. The erecting member may be an adhesive tapeor a roller.

The method may further comprise fixing the cathode to a cathode base.The fixing of the cathode may be performed between the transferring ofthe electron emission material layer and the performing of the tapingprocess.

The suspension may include a solvent and a surfactant.

According to another aspect of the present invention, there is provideda display apparatus comprising: a cathode fixed to a top surface of asubstrate; a plurality of electron emission material layers formed atpredetermined intervals on a top surface of the cathode; an adhesivelayer fixing the electron emission material layers to the cathode; afront plate spaced apart from the substrate; an anode formed on an innersurface of the front plate facing the electron emission material layers;a phosphor layer formed on a surface of the anode; a grid disposedbetween the cathode and the phosphor layer and extracting electrons fromthe electron emission material layers; and an insulating layer havingthrough-holes corresponding to the electron emission material layers andformed on the cathode.

The cathode may be fixed to the substrate by an adhesive layer disposedunder the cathode.

An adhesive layer for fixing the electron emission material layers tothe cathode may be formed only under the electron emission materiallayers.

An adhesive layer for adhering the electron emission material layers andan adhesive layer for fixing the cathode to the substrate may be formedon both surfaces of the cathode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a perspective view of a unit electron emission sourceaccording to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of the electron emission source of FIG.1 according to an embodiment of the present invention;

FIG. 3 is a cross-sectional view of a cathode of the electron emissionsource of FIG. 1 according to an embodiment of the present invention;

FIG. 4 illustrates various cathode bases supporting the cathode of theelectron emission source of FIG. 1 according to embodiments of thepresent invention;

FIG. 5A is a perspective view of an electron emission source accordingto another embodiment of the present invention;

FIG. 5B is a side view of the electron emission source of FIG. 5Aaccording to an embodiment of the present invention;

FIG. 6A is a perspective view of an electron emission source accordingto another embodiment of the present invention;

FIG. 6B is a side view of the electron emission source of FIG. 6Aaccording to an embodiment of the present invention;

FIG. 7A is a perspective view of an electron emission source accordingto another embodiment of the present invention;

FIG. 7B is a side view of the electron emission source of FIG. 7Aaccording to an embodiment of the present invention;

FIG. 8 is a perspective view of an electron emission source according toanother embodiment of the present invention;

FIGS. 9A through 9F are cross-sectional views illustrating a method ofmanufacturing an electron emission source according to an embodiment ofthe present invention;

FIGS. 10A and 10B are scanning electron microscopy (SEM) images of acarbon nanotube (CNT) layer before and after the CNT layer is subjectedto a taping process;

FIG. 11 is a graph illustrating a relationship between electric fieldand current density before and after a CNT layer of a CNT field electronemission source is subjected to a taping process;

FIG. 12 is a graph illustrating a relationship between current densityand electric field after a CNT field electron emission source issubjected to a surface protrusion process when a CNT suspension is atdifferent concentrations;

FIG. 13 is a graph illustrating a relationship between field enhancementfactor and turn-on electric field, threshold electric field, maximumelectric field, and concentration of a CNT colloidal suspension;

FIGS. 14A, 14B, and 14C are optical photographs illustrating abrightness difference between three samples with different luminousareas manufactured according to the present invention;

FIG. 15 is a graph illustrating results of an electron emissionstability test on different types of CNTs;

FIG. 16 is a plan view illustrating cathodes of a display apparatusaccording to an embodiment of the present invention;

FIG. 17 is a cross-sectional view taken along line A-A′ of FIG. 16according to an embodiment of the present invention;

FIG. 18 is a cross-sectional view of a display apparatus according to anembodiment of the present invention;

FIG. 19A is a cross-sectional view illustrating a method ofmanufacturing a cathode of a display apparatus according to anembodiment of the present invention; and

FIG. 19B is a cross-sectional view illustrating a method ofmanufacturing a cathode of a display apparatus according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which embodiments of the invention are shown.This should not be construed as limiting the claims to the embodimentsshown. Rather, these embodiments are provided to convey the scope of theinvention to those skilled in the art. In the drawings, the size andrelative sizes of elements and regions may be exaggerated for clarity.

It will be understood that when an element or layer is referred to asbeing “on”, “interposed”, “disposed”, or “between” another element orlayer, it can be directly on, interposed, disposed, or between the otherelement or layer or intervening elements or layers can be present.

The terms “first,” “second,” and the like, “primary,” “secondary,” andthe like, as used herein do not denote any order, quantity, orimportance, but rather are used to distinguish one element, region,component, layer, or section from another. The terms “front”, “back”,“bottom”, and/or “top” are used herein, unless otherwise noted, merelyfor convenience of description, and are not limited to any one positionor spatial orientation.

The terms “a” and “an” do not denote a limitation of quantity, butrather denote the presence of at least one of the referenced item. Thesuffix “(s)” as used herein is intended to include both the singular andthe plural of the term that it modifies, thereby comprising one or moreof that term (e.g., the layer(s) includes one or more layers).

Reference throughout the specification to “one embodiment”, “anotherembodiment”, “an embodiment”, and so forth, means that a particularelement (e.g., feature, structure, and/or characteristic) described inconnection with the embodiment is included in at least one embodimentdescribed herein, and may or may not be present in other embodiments. Inaddition, it is to be understood that the described elements may becombined in any suitable manner in the various embodiments.

The endpoints of all ranges directed to the same component or propertyare inclusive of the endpoint and independently combinable, e.g., rangesof “up to about 25 wt. %, or, more specifically, about 5 wt. % to about20 wt. %,” is inclusive of the endpoints and all intermediate values ofthe ranges of “about 5 wt. % to about 25 wt. %,” etc. The modifier“about” used in connection with a quantity is inclusive of the statedvalue and has the meaning dictated by the context (e.g., includes thedegree of error associated with measurement of the particular quantity).

Unless defined otherwise, technical and scientific terms used hereinhave the same meaning as is commonly understood by one of skill in theart to which this invention belongs.

FIG. 1 is a perspective view of a unit electron emission source 10according to an embodiment of the present invention. FIG. 2 is across-sectional view of the electron emission source 10 of FIG. 1.

The electron emission source 10 uses needle-shaped electron emissionmaterials. Examples of the needle-shaped electron emission materialsinclude hollow nanotubes or filled nanorods, e.g., carbon nanotubes orcarbon nanorods, or other metal materials. Carbon nanotubes (CNTs),which are representative needle-shaped electron emission materials, willbe exemplarily explained. However, the present invention is not limitedthereto and any needle-shaped materials capable of emitting electronscan be used.

Referring to FIGS. 1 and 2, the electron emission source 10 includes aplate-shaped cathode 11 to which a CNT layer 13 is fixed by an adhesivelayer 12, and a cathode base 14 supporting the cathode 11. The cathode11 includes a ring-shaped fixing member 15. The fixing member 15 isforcedly fitted around a protrusion 14 a of the base 14 to fixedlycompress a skirt portion 11 a of the cathode 11. The plate-shapedcathode 11 is formed of a plate-shaped conductive material that isseparately manufactured from the base 14. The adhesive layer 12 isformed on a surface of the cathode 11, such that CNTs of the CNT layer13 having lower ends contacting the adhesive layer 12 are stronglyattached to the cathode 11. The CNT layer 13 is formed fromsubstantially pure CNTs, and thus has higher stability and reliabilitythan a conventional CNT layer formed of CNT paste. Since the CNT layer13 formed on the plate-shaped cathode 11 is fixed to the base 14 that isa support structure of the electron emission source 10, a manufacturingprocess is simple. Also, since a high temperature process is notrequired, there is no financial burden accompanying the high temperatureprocess. In particular, since the adhesive layer 12 which may includeorganic matters is formed only under the CNTs, the risk of collisionsbetween the organic matters and electrons is very low, and thus organicgas is hardly generated.

FIG. 3 is a cross-sectional view of the cathode 11 of the electronemission source 10 according to another embodiment of the presentinvention. Referring to FIG. 3, since another adhesive layer 12 a isformed on a bottom surface of the plate-shaped cathode 11, the cathode11 can be more securely fixed to the cathode base 14 due to the adhesivelayer 12 a. The adhesive layer 12 disposed between the cathode 11 andthe CNT layer 13 and fixing the CNTs of the CNT layer 13 to the cathode11 may be a material layer already formed on a surface of theplate-shaped cathode 11. That is, the plate-shaped cathode 11 may bemanufactured to have both surfaces to which the adhesive layers 12 and12 a are applied and then may be used for the electron emission source10. The upper adhesive layer 12 for fixing the CNTs to the cathode 11may be formed only under the CNT layer 13, or alternatively, may beformed over an entire top surface of the cathode 11. The adhesive layer12 is formed only under the CNT layer 13 in FIG. 1.

The fixing member 15 for fixing the cathode 11 to the cathode base 14 isoptional. The base 14 and the fixing member 15 are complimentarilyengaged with each other such that the cathode base 14 and the fixingmember 15 can securely fix the cathode 11 between the cathode base 14and the fixing member 15. FIG. 4 illustrates various cathode basesaccording to embodiments of the present invention. Referring to FIG. 4,the protrusion 14 a may have a polygonal shape, such as a square, adiamond, a triangle, or a pentagon, an oval shape, or other variousshapes such as a letter, a number, or a symbol. The fixing member 15 mayhave a conformal shape to engage with the protrusion 14 a.

FIG. 5A is a perspective view of an electron emission source accordingto another embodiment of the present invention. FIG. 5B is a side viewof the electron emission source of FIG. 5A according to an embodiment ofthe present invention. Referring to FIGS. 5A and 5B, without using thefixing member 15, a cathode 111 to which a CNT layer 113 is fixed by anadhesive layer 112 may be directly welded to a cathode base 114. Thecathode 111 has a band shape, and the cathode base 114 includes aprotrusion 114 a having an angular side surface. The electron emissionsource is formed by first forming the CNT layer 113 on the cathode 111,pulling out both ends of the cathode 111 with an appropriate tensileforce, and welding the cathode 111 to the protrusion 114 a of thecathode base 114. In FIGS. 5A and 5B, reference numeral 111 a denotes awelding point or a welding portion having a predetermined length.Without using the fixing member 15 shown in FIGS. 1 and 2, the cathode111 of FIGS. 5A and 5B is directly fixed to the cathode base 114.

FIGS. 6A and 7A are perspective views of electron emission sourcesaccording to other embodiments of the present invention. FIGS. 6B and 7Bare cross-sectional views of the electron emission sources of FIGS. 6Aand 7A, respectively, according to embodiments of the present invention.

The electron emission source of FIGS. 6A and 6B is similar in structureto the electron emission source of FIGS. 5A and 5B. A protrusion 124 aof a cathode base 124 has a curved side surface that is partiallysurrounded by a cathode 121. The cathode 121 has a band shape, and thecathode base 124 includes the protrusion 124 a having the curved sidesurface. The electron emission source of FIGS. 6A and 6B is formed byfixing a CNT layer 123 to the cathode 121 by using an adhesive layer122, pulling out both ends of the cathode 121 with an appropriatetensile force, and welding the cathode 121 to welding portions 121 athat are formed at lower sides of the protrusion 124 a of the cathodebase 124.

Referring to FIGS. 7A and 7B, a cylindrical protrusion 134 a of acathode base 134 has a curved side surface. A CNT layer 133 is locatedon a cathode 131 corresponding to the protrusion 134 a. The CNT layer133 is fixed to the cathode 131 by using an adhesive layer 132.

A lower skirt portion 131 a of the cathode 131 is strongly pressed tothe protrusion 134 a by a fixing member 135. The cathode 131 may beformed of a flexible material, such as aluminum, so that the cathode 131can be closely attached to the protrusion 134 a having the curved sidesurface. The cathode may have a wrinkle portion 131 b in the lower skirtportion 131 a.

FIG. 8 is a perspective view of an electron emission source according toanother embodiment of the present invention. A cathode 141 is welded toa plate-shaped cathode base 144. In detail, the cathode 141 has a diskshape, and a CNT layer 143 is formed on a central portion of the cathode141. A skirt portion 141 a of the cathode 141 is welded to a top surfaceof the cathode base 144. In FIG. 8, reference numeral 141 b denotes awelding portion.

In the aforementioned embodiments, although the cathodes 111 and 141 arerespectively welded to the cathode bases 114 and 144, adhesive layersmay be formed under the cathodes 111 and 141 so that the cathodes 114and 141 can be more securely and stably fixed to the cathode bases 114and 144.

The unit electron emission sources may be applied to electronic devicesin various fields. Examples of the electron devices include a visiblelight source used for illumination, a backlight unit for a flat paneldisplay (FPD), an electronic source for an X-ray device, and anelectronic device for high power microwaves.

In the above embodiments, the cathodes 11, 111, 121, 131, and 141 areconductors having properly adjusted electrical resistances, such thatcurrent is uniformly supplied to the CNT layers 13, 113, 123, 133, and143 fixed to the surfaces of the cathodes 11, 111, 121, 131, and 141 andthe CNT layers 13, 113, 123, 133, and 143 can uniformly emit electrons.

FIGS. 9A through 9F are cross-sectional views illustrating a method ofmanufacturing a unit electron emission source according to an embodimentof the present invention.

First, a CNT colloidal suspension (referred to as a suspension), and afilter template formed of Teflon, ceramic, anodic aluminum oxide (AAO),or polycarbonate are prepared. The suspension is a colloidal solutionformed by dispersing CNT powder in a solvent and a surfactant. For moreeven dispersion, ultrasonic treatment may be performed. The suspensionis filtered through the filter template and only CNTs are left behind ona surface of the filter template. The suspension is dried, and only theleft CNTs are patterned and transferred to a plate-shaped cathode. TheCNTs may be single-walled (SW) CNTs, double-walled (DW) CNTs, thinmulti-walled (MW) CNTs, or thick MWCNTs. The solvent is any one selectedfrom the group consisting of ethanol, dimethyl formamide,tetrahydrofuran, dimethyl acetamide, 1,2 dichloroethane, and 1,2dichlorobenzene.

The surfactant is any one selected from the group consisting of sodiumdodecylbenzene sulfonate (NaDDBS C1₂H₂₅C₆H₄SO₃Na), sodium butylbenzenesulfonate (NaBBS C₄H₉C₆H₄SO₃Na), sodium benzoate(C₆H₅CO₂Na), sodiumdodecyl sulfate (SDS; CH₃(CH₂)₁₁OSO₃Na), Triton X-100 (TX100;C₈H₁₇C₆H₄(OCH₂CH₂)n-OH; n 10), dodecyltrimethylammonium bromide (DTAB;CH₃(CH₂)₁₁N(CH₃)₃Br), and arabic gum.

Referring to FIG. 9A, a suspension is filtered through a filter template21, patterned into a predetermined shape, and dried to form a CNT layer13′. The predetermined shape corresponds to the shape of a cathode 11 ofthe electron emission source, for example, any one of the various shapesshown in FIG. 4. The predetermined shape varies depending on the shapeof the cathode 11. Here, by controlling a solvent and a surfactant ofthe suspension and the concentration of CNTs, CNT density can be freelycontrolled and optimal electron emission under various surroundingelectrical conditions can be obtained, and thus a CNT layer with goodreproduction, high uniformity, and optimal density can be formed. Thesuspension is applied to the filter template 21, only the CNTs are leftbehind, and a liquid material is passed through the filter template 21.When a drying process is performed in this state, the CNT layer 13′ isformed on the surface of the filter template 21. Air drying or vacuumdrying may be performed at room temperature or at high temperature.

Referring to FIG. 9B, the cathode 11 having both surfaces on which upperand lower adhesive layers 12 and 12 a are disposed is prepared. Thelower adhesive layer 12 a is protected by release paper (not shown) forpreventing foreign particles from sticking to the lower adhesive layer12 a. The cathode 11 is formed of a conductive material such as aconductive fabric or a metal plate. The upper and lower adhesive layers12 and 12 a may be formed of a conductive material such as a mixture ofmodified nickel and a polymer resin. In detail, the cathode 11 is formedof an aluminum foil having a thickness of 0.01 to 0.04 mm, or aconductive sheet including copper or nickel and having a thickness of0.01 to 0.04 mm, or a conductive fabric having a thickness of 0.01 to0.20 mm. That is, the cathode 11 may be formed of any one of aconductive fabric and a conductive sheet including any one of aluminum,copper, and nickel.

Each of the upper and lower adhesive layers 12 and 12 a is formed of amixture of conductive powder, such as nickel or carbon black, and anadhesive resin, such as acrylic ester polyol copolymer. Each of theupper and lower adhesive layers 12 and 12 a is a conductive tape havinga contact resistance of less than 0.1 Ω/25 mm² and an allowabletemperature of −30° C. to 105° C.

Referring to FIG. 9C, the CNT layer 13′ on the filter template 21 isbrought into contact with the upper adhesive layer 12 of the cathode 11at a predetermined pressure, and then the filter template 21 isseparated from the CNT layer 13′ to form a CNT layer 13 for electronemission on the cathode 11.

FIG. 9D illustrates that the CNT layer 13 is subjected to a tapingprocess such that CNTs of the CNT layer 13 which are randomly arrangedon the cathode 11 are vertically aligned. Referring to FIG. 9D-(a), anadhesive tape 22 is adhered to the CNT layer 13 on the cathode 11, andthen is pulled up to strip off from the CNT layer 13. As such, exposedCNTs on a surface of the CNT layer 13 are vertically erected to thecathode 11 due to the adhesive tape 22. That is, the CNTs are erected ina direction perpendicular to the cathode 11 by means of the tape 22.Instead of the tape 22, an adhesive roller 23 may be used as shown inFIG. 9D-(b). Referring to FIG. 9D-(b), the adhesive roller 23 is rolledover the surface of the CNT layer 13 at a predetermined pressure, suchthat the CNTs are vertically erected to the cathode 11. During thetaping process, some of the CNTs weakly fixed to the upper adhesivelayer 12 of the cathode 11 may be separated and removed from the cathode11. However, since most of the CNTs are strongly fixed to the cathode11, the CNTs are vertically erected.

FIG. 9E illustrates that the cathode 11 is coupled to a cathode base 14.Referring to FIG. 9E, the cathode base 14 having a protrusion 14 a isprepared, and then the cathode 11 is mounted on the cathode base 14. TheCNT layer 13 formed on the cathode 11 is located to correspond to a topsurface of the protrusion 14 a. In this state, a fixing member 15 havinga coupling hole 15 a corresponding to the protrusion 14 a is prepared.For clarity, the thicknesses of the cathode 11 and the upper and loweradhesive layers 12 and 12 a of FIGS. 9C through 9E are exaggerated.

Referring to FIG. 9F, the fixing member 15 is fitted around theprotrusion 14 a, to fix the cathode 11 to the cathode base 14. Thefixing member 15 fixes a skirt portion 11 a of the cathode 11 around theprotrusion 14 a, thereby obtaining a desired single electron emissionsource 10. The upper and lower adhesive layers 12 and 12 a formed onboth the surfaces of the cathode 11 are not shown in FIG. 9F.

The method of FIGS. 9A through 9F may be modified in various ways. Forexample, the taping process for vertically erecting the CNTs of the CNTlayer 13 may be performed in the state where the cathode 11 is fixed tothe cathode base 14. That is, after the operations of 9C, 9E, and 9F areperformed, the taping process of FIG. 9D-(a) using the adhesive tape 22or of FIG. 9D-(b) using the adhesive roller 23 may be performed.However, the present invention is not limited to the taping process ofFIG. 9D, and various modifications can be made without departing fromthe scope of the present invention.

The electron emission source according to the present invention ischaracterized in that after a CNT layer is fixed to a surface of acathode, which is a plate-shaped conductor, by an adhesive layer, thecathode is fixed to a cathode base. That is, unlike a conventionalelectron emission source in which a cathode is fixed to a substrate andthen CNTs are grown or fixed to the cathode, the electron emissionsource according to the present invention is characterized in that thata CNT layer is formed on a plate-shaped cathode and then the cathode iscoupled to a substrate or a cathode base supporting the cathode. Each ofthe cathode bases in the above embodiments may correspond to thesubstrate of the conventional electron emission source. Unlike theconventional electron emission source in which the CNTs and paste aremixed, the electron emission source according to the present inventionis also characterized in that an adhesive layer is disposed only underCNTs and the CNTs are fixed to the cathode due to the adhesive layer.

A method of manufacturing the electron emission sources shown in FIGS.5A, 5B, 6A, and 6B would have been easily derived from the method ofFIGS. 9A through 9F.

FIGS. 10A and 10B are scanning electron microscopy (SEM) images andemission patterns of a CNT layer before and after the CNT layer issubjected to a taping process. Referring to FIG. 10A, most of CNTs aretangled and lie down like a net and some of the CNTs are sparselystanding. In order to test electric field electron emission uniformity,a field emission pattern test was performed on a structure including ananode, which was formed by applying a phosphor to a transparent glasscoated with indium tin oxide (ITO), and a cathode using a CNT layer thatwas not subjected to a taping process. A distance between the anode andthe cathode was 400 μm. Referring to the emission pattern image shown atan upper right corner of FIG. 10A, partial emission, not a completeemission, is observed. This is because most of the CNTs lie down and thenumber of CNTs contributing to field electron emission is low. However,referring to FIG. 10B, since the taping process is performed, CNTs arevertically erected to uniform heights. Referring to the emission patternimage at an upper right corner of FIG. 10B, complete emission, notpartial emission, is observed. This is because most of the CNTs arevertically erected, and when an electric field is applied, the electricfield concentrates on tips of the vertically erected CNTs, therebyresulting in easy field electron emission and uniform electron emission.

FIG. 11 is a graph illustrating a relationship between current density J(A/cm²) and electric field F (V/μm) before and after a CNT layer of aCNT electron emission source is subjected to a taping process. A fieldelectron emission test was performed on a structure including an anode,which was a stainless steel plate, and a cathode, which was a CNT fieldelectron emission source. A distance between the anode and the cathodewas 400 μm, and an electron emission area was 0.19625 cm². A vacuumlevel was 2×10⁻⁷ torr, and an applied voltage ranged from 0 V to 3500 V.CNT powder used for the CNT electric field emission source was athin-MWCNT having an average diameter of approximately 7 nm. A CNTcolloidal suspension was at a concentration of 20 mg/l. A turn-onelectric field necessary to obtain a current density of 0.1 μA/cm²before and after a taping process was 1.24 V/μm and 0.88 V/μm, and anelectric field necessary to obtain a maximum current density of 10mA/cm² before and after a taping process was 2.70 V/μm and 1.98 V/μm. Itcan be seen that higher electric field electron emission characteristicsat a low electric field can be obtained after the taping process thanbefore the taping process. Also, it can be seen that since adhesionbetween the cathode formed of a conductive tape and the CNT layer ishigh after the taping process, stable electric field electron emissioncan be achieved even at a high electric field. A graph embedded in FIG.11 is a Fowler-Nordheim plot illustrating a relationship between currentdensity and electric field before and after of a CNT layer of a CNTfield electron emission source is subjected to a taping process using anadhesive tape. Electric emission generally obeys the Fowler-Nordheimequation, and current density J is given by J=a(E_(loc)²/φ)exp(−bφ^(3/2)/E_(loc)) where a and b are constants, Φ is a workfunction (ev), E_(loc) is an electric field applied to a tip of the CNTfield electron emission source and satisfies E_(loc)=β F (β: fieldenhancement factor), and F=V/d (V: a voltage between the anode and thecathode, and d: a distance between the anode and the cathode).Accordingly, in order to obtain a high current density J, the electricfield E_(loc) applied to the tip of the CNT field electron emissionsource must be maximized and the work function Φ must be minimized.However, when the electric field E_(loc) applied to the tip of the CNTfield electron emission source is high, the tip of the CNT fieldelectron emission source may be deteriorated and deformed and electricfield emission characteristics may be deteriorated, thereby loweringefficiency. It is most effective to change the shape of the CNT electronemission source. The field enhancement factor β, which is related to theshape of the CNT electron emission source, is a proportional constantfor the electric field E_(loc) applied to the tip of the CNT fieldelectron emission source and the electric field F applied between theanode and the cathode. Since the field enhancement factor β is relatedto the shape of the CNT field electron emission source, the fieldenhancement factor β increases as an aspect ratio increases.Accordingly, although the electric field F applied between the anode andthe cathode is the same, the electric field E_(loc) applied to the tipof the CNT field electron emission source is high, thereby improvingelectric field emission characteristics. Referring to theFowler-Nordheim plot of FIG. 11, an almost vertical gradient is shownwhen an electric field is low, and field electron emissioncharacteristics and the field enhancement factor β can be obtained fromthe gradient. The field enhancement factor β was 2338 before the tapingprocess and 3337 after the taping process. It can be seen that CNTslying down before the taping process are vertically aligned after thetaping process to increase the field enhancement factor β and improveelectric field emission characteristics.

FIG. 12 is a graph illustrating current density and electric field aftera CNT field electron emission source is subjected to a surfaceprotrusion process when a CNT suspension is at different concentrations.After a test was performed on samples having CNT suspensions atconcentrations of 1.25, 2.5, 5.0, 10, and 20 mg/l, it is found that aturn-on electric field and a maximum current density are obtained at alow electric field. After a test was performed on samples having CNTsuspensions at concentrations of 40 and 80 mg/l, it is found that theintensity of an electric field necessary to obtain a turn-on electricfield and a maximum current density is saturated at a level similar tothat when the CNT colloidal suspension is at the concentration of 20mg/l. Accordingly, when the colloidal suspension has a concentration of20 mg/l, high electric field electron emission characteristics areobtained, and the present invention can easily control optimal CNT fieldelectron emission density. A graph embedded in FIG. 12 is aFowler-Nordheim plot illustrating a relationship between current densityand electric field after a surface protrusion process when a CNTsuspension is at different concentrations. After the test was performedon the samples having the CNT suspensions at concentrations of 1.25,2.5, 5.0, 10, and 20 mg/l, it is found that the field enhancement factorβ increases as the concentration increases. After the test was performedon the samples having the CNT suspensions at concentrations of 40 and 80mg/l, it is found that the field enhancement factor β is saturated at alevel similar to that the intermediate CNT colloidal suspension is atthe concentration of 20 mg/l. Accordingly, optimal field electronemission density and maximum field emission characteristics can beobtained by controlling the concentration of the CNT suspension.

FIG. 13 is a graph illustrating a relationship between field enhancementfactor β, turn-on electric field, a threshold electric field, maximumelectric field, and concentration of a CNT colloidal suspension.

FIGS. 14A, 14B, and 14C are optical photographs illustrating abrightness difference between three samples with different luminousareas manufactured according to the present invention.

CNT layers of FIGS. 14A through 14C had diameters of 5 mm (0.19625 cm²),10 mm (0.785 cm²), and 20 mm (3.14 cm²), respectively. The electronemission source shown in FIG. 1 was used, an anode formed by coating aphosphor to a transparent glass coated with ITO was used, a distancebetween the anode and a cathode was 400 μm, a vacuum level was 2×10⁻⁷torr, and an applied voltage ranged from 0 V to 3500 V. It can be seenfrom FIGS. 14A through 14C that very satisfactory luminous efficiency,that is, very uniform brightness, is achieved, and even when a luminousarea increases, very high luminous efficiency is achieved.

FIG. 15 is a graph illustrating results of an electron emissionstability test on different types of CNTs. It can be seen from FIG. 15that MWCNTs are more stable than DWCNTs.

The afore-described single electron emission source may be applied to adisplay apparatus. In general, display apparatuses have pixels that areelectrically addressed in an X-Y matrix, stripe-like cathodes spanningthe width of a screen are arranged in parallel, and CNT layers areformed on surfaces of the cathodes to correspond to the pixels.

FIG. 16 is a plan view illustrating cathodes 31 arranged on a substrate30 of a display apparatus according to an embodiment of the presentinvention. FIG. 17 is a cross-sectional view taken along line A-A′ ofFIG. 16 according to an embodiment of the present invention. CNT layers32 are formed on surfaces of the cathodes 31 at intervals correspondingto pitches of pixels of the display apparatus. The cathodes 31 areformed of a conductive material or a material with an electricalresistance. After separately manufactured, the cathodes 31 are fixed tothe substrate 30 by welding or by using adhesive layers 31 b. The CNTlayers 32 are fixed to top surfaces of the cathodes 31 by using adhesivelayers 31 a formed under the CNT layers 32. The adhesive layer 31 a forfixing the CNT layers 32 to the cathodes 31 may be formed on the entiretop surfaces of the cathodes 31 as shown in FIG. 16, or may be formedonly under the CNT layers 32.

FIG. 18 is a cross-sectional view of a display apparatus according to anembodiment of the present invention.

Referring to FIG. 18, a cathode 31 is attached to a top surface of asubstrate 30, which is a rear plate, by using an adhesive layer 31 b.The adhesive layer 31 b is an optional element for fixing the cathode 31to the substrate 30. When the adhesive layer 31 b is not used, thecathode 31 may be fixed to the substrate 30 by welding or other adhesionmethods as described in the above embodiments. A CNT layer 32 is formedon a top surface of the cathode 31. The CNT layer 32 is fixed to thecathode 31 by using an adhesive layer 31 a that is formed under the CNTlayer 32. The cathode 31 is separately manufactured from the substrate30, and then is fixed to the substrate 30 by using the adhesive layer 31a or other means. The CNT layer 32 may be fixed to the cathode 31 in theaforementioned manufacturing method. An insulating layer 40 having athrough-hole through which the CNT layer 32 is to be passed is formed onthe cathode 31, and a grid 41 for extracting electrons is disposed onthe insulating layer 40. A front plate structure is separatelymanufactured, and then is integrally coupled to the grid 41. The frontplate structure includes a front plate 50 and an anode 51 formed on aninner surface of the front plate 50. A phosphor layer 52 is formed on asurface of the anode 51.

The CNT layer 32 disposed on the cathode 31 is manufactured by using aCNT suspension. Since a plurality of CNT layers 32 are disposed on oneband-shaped cathode 31, it is necessary to apply a CNT suspension to aplurality of regions of a filter template corresponding to the onecathode 31. To this end, the CNT suspension may be supplied to only thegiven regions of the cathode 31 by using a printing method or a mask.

FIG. 19A is a cross-sectional view illustrating a method ofmanufacturing a cathode of a display apparatus according to anembodiment of the present invention. FIG. 19B is a cross-sectional viewillustrating a method of manufacturing a cathode of a display apparatusaccording to another embodiment of the present invention. Referring toFIG. 19A, a CNT suspension is supplied to a band-shaped filter template60 through a nozzle. The CNT suspension is dried, and then istransferred, to obtain a cathode 31 having CNT layers 32 as shown inFIGS. 16, 17, and 18. Alternatively, a suspension may be supplied at onetime as shown in FIG. 19B. Referring to FIG. 19B, a mask 80 havingthrough-holes corresponding to CNT layers is placed over a filtertemplate 60 and then a CNT suspension 32″ is supplied. Accordingly, theCNT suspension 32″ can be supplied to given regions of the filtertemplate 60 in a short time. In this case, since the CNT suspension 32″is in contact with the mask 80, when the mask 80 is separated from thefilter template 60 before the CNT suspension 32″ is dried, the CNTsuspension 32″ is stuck a little to the mask 80, thereby failing to formcomplete CNT layers on the filter template 60. Accordingly, it ispreferable that after the CNT suspension 32″ is properly or completelydried, the mask 80 should be separated from the filter template 60. Theplurality of CNT layers are formed on the filter template 60 in thisway, and then are transferred to the cathode.

Accordingly, a CNT thin film formed by using a suspension filteringmethod can be easily transferred by using a conductive tape with strongadhesion. Since adhesion between the CNT thin film and the conductivetape is very high, field electron emission characteristics of the CNTthin film can be improved by a simple taping process. Stable andreliable electric field electron emission characteristics can beobtained without attaching or detaching the CNT thin film duringelectric field electron emission even at a high electric field. Theactive electron emission site density of the CNT thin film can be easilycontrolled by controlling the concentration of an evenly dispersed CNTcolloidal suspension. Also, a large CNT thin film with uniformcharacteristics can be easily manufactured by using this method, andthus a large CNT field electron emission source can be manufactured.

As described above, according to the present invention, a CNT layerhaving an optimal concentration for electric field electron emission isformed by preparing an evenly dispersed CNT colloidal suspension byusing any of various types of needle-shaped electron emission materials,that is, nanotubes or nanorods having a predetermined length, forexample, CNT powder, through a suspension filtering method, supplyingthe suspension onto a filter template having pores, filtering thesuspension through the filter template, and drying the suspension. SinceCNTs are very uniformly dispersed in the suspension, the CNT layerformed on the filter template can have uniform CNTs. Since the CNT layeris transferred to a cathode on which an adhesive layer is formed, theCNT layer can be stably fixed to the cathode. Since the CNT layer issubjected to a subsequent taping process such that the CNTs arevertically erected to the cathode, the number of CNTs contributing toelectron emission can be drastically increased. Since the CNT layer canbe formed on the cathode at low temperature or room temperature, not athigh temperature, problems that a conventional high temperature processencounters can be avoided. Accordingly, the electron emission sourceaccording to the present invention can be structurally very stable andcan ensure high and uniform electron emission.

Since the electron emission source according to the present inventioncan be simply manufactured at room temperature without a complicatedprocess without using paste including conductive organic/inorganicmatters, binders, and polymers which badly affect field electronemission characteristics, a large electron emission source can bemanufactured. In particular, since a large electron emission area can beeasily obtained, a display apparatus can have one CNT layer at onepixel.

Since the CNT layer is formed by using the suspension, the concentrationof the CNT layer can be easily controlled by controlling theconcentration of the CNTs, and accordingly, optimal field electronemission source density can be obtained.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. A method of manufacturing an electron emissionsource, the method comprising: forming an electron emission materiallayer on a template; transferring the electron emission material layerto a plate-shaped cathode on which an adhesive layer is formed; andperforming a surface treatment process on the electron emission materiallayer transferred to the cathode to erect electron emission materialswith respect to the cathode.
 2. The method of claim 1, wherein thetemplate is a filter template having filterability.
 3. The method ofclaim 1, wherein the forming of the electron emission material layer onthe template comprises: applying a suspension in which electron emissionmaterials are dispersed onto the template; and drying the suspension. 4.The method of claim 1, further comprising fixing the cathode to a basethat supports the cathode.
 5. The method of claim 1, wherein the surfacetreatment process uses any one selected from the group consisting amethod using an adhesive tape, a roller rubbing method, an ion beamemitting method, a plasma treatment method, a laser beam emittingmethod, a neutron beam emitting method, and a hydrogen gas exposingmethod.
 6. The method of claim 3, wherein the suspension includes asolvent and a surfactant.
 7. A method of manufacturing a displayapparatus comprising a front plate on which an anode is formed and asubstrate on which a cathode is formed, the method comprising: forming aplurality of electron emission material layers at predeterminedintervals on a band-shaped template; transferring the electron emissionmaterial layers to a band-shaped cathode on which an adhesive layer isformed; performing a taping process on the electron emission materiallayers transferred to the cathode to erect electron emission materialswith respect to the cathode; and fixing the cathode to a rear plate. 8.The method of claim 7, wherein the template is a filter template havingfilterability.
 9. The method of claim 7, wherein the forming of theplurality of electron emission material layers on the templatecomprises: applying a suspension in which electron emission materialsare dispersed onto the template; and drying the suspension.
 10. Themethod of claim 7, wherein an adhesive layer to which the electronemission material layers are fixed is formed on a side surface of thecathode.